<HTML>
<BODY BGCOLOR="white">
<PRE>
<FONT color="green">001</FONT>    /*<a name="line.1"></a>
<FONT color="green">002</FONT>     * Licensed to the Apache Software Foundation (ASF) under one or more<a name="line.2"></a>
<FONT color="green">003</FONT>     * contributor license agreements.  See the NOTICE file distributed with<a name="line.3"></a>
<FONT color="green">004</FONT>     * this work for additional information regarding copyright ownership.<a name="line.4"></a>
<FONT color="green">005</FONT>     * The ASF licenses this file to You under the Apache License, Version 2.0<a name="line.5"></a>
<FONT color="green">006</FONT>     * (the "License"); you may not use this file except in compliance with<a name="line.6"></a>
<FONT color="green">007</FONT>     * the License.  You may obtain a copy of the License at<a name="line.7"></a>
<FONT color="green">008</FONT>     *<a name="line.8"></a>
<FONT color="green">009</FONT>     *      http://www.apache.org/licenses/LICENSE-2.0<a name="line.9"></a>
<FONT color="green">010</FONT>     *<a name="line.10"></a>
<FONT color="green">011</FONT>     * Unless required by applicable law or agreed to in writing, software<a name="line.11"></a>
<FONT color="green">012</FONT>     * distributed under the License is distributed on an "AS IS" BASIS,<a name="line.12"></a>
<FONT color="green">013</FONT>     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.<a name="line.13"></a>
<FONT color="green">014</FONT>     * See the License for the specific language governing permissions and<a name="line.14"></a>
<FONT color="green">015</FONT>     * limitations under the License.<a name="line.15"></a>
<FONT color="green">016</FONT>     */<a name="line.16"></a>
<FONT color="green">017</FONT>    package org.apache.commons.math.stat.descriptive.moment;<a name="line.17"></a>
<FONT color="green">018</FONT>    <a name="line.18"></a>
<FONT color="green">019</FONT>    import java.io.Serializable;<a name="line.19"></a>
<FONT color="green">020</FONT>    <a name="line.20"></a>
<FONT color="green">021</FONT>    import org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic;<a name="line.21"></a>
<FONT color="green">022</FONT>    import org.apache.commons.math.stat.descriptive.summary.Sum;<a name="line.22"></a>
<FONT color="green">023</FONT>    <a name="line.23"></a>
<FONT color="green">024</FONT>    /**<a name="line.24"></a>
<FONT color="green">025</FONT>     * &lt;p&gt;Computes the arithmetic mean of a set of values. Uses the definitional <a name="line.25"></a>
<FONT color="green">026</FONT>     * formula:&lt;/p&gt;<a name="line.26"></a>
<FONT color="green">027</FONT>     * &lt;p&gt;<a name="line.27"></a>
<FONT color="green">028</FONT>     * mean = sum(x_i) / n<a name="line.28"></a>
<FONT color="green">029</FONT>     * &lt;/p&gt;<a name="line.29"></a>
<FONT color="green">030</FONT>     * &lt;p&gt;where &lt;code&gt;n&lt;/code&gt; is the number of observations.<a name="line.30"></a>
<FONT color="green">031</FONT>     * &lt;/p&gt;<a name="line.31"></a>
<FONT color="green">032</FONT>     * &lt;p&gt;When {@link #increment(double)} is used to add data incrementally from a<a name="line.32"></a>
<FONT color="green">033</FONT>     * stream of (unstored) values, the value of the statistic that <a name="line.33"></a>
<FONT color="green">034</FONT>     * {@link #getResult()} returns is computed using the following recursive<a name="line.34"></a>
<FONT color="green">035</FONT>     * updating algorithm: &lt;/p&gt;<a name="line.35"></a>
<FONT color="green">036</FONT>     * &lt;ol&gt;<a name="line.36"></a>
<FONT color="green">037</FONT>     * &lt;li&gt;Initialize &lt;code&gt;m = &lt;/code&gt; the first value&lt;/li&gt;<a name="line.37"></a>
<FONT color="green">038</FONT>     * &lt;li&gt;For each additional value, update using &lt;br&gt;<a name="line.38"></a>
<FONT color="green">039</FONT>     *   &lt;code&gt;m = m + (new value - m) / (number of observations)&lt;/code&gt;&lt;/li&gt;<a name="line.39"></a>
<FONT color="green">040</FONT>     * &lt;/ol&gt;<a name="line.40"></a>
<FONT color="green">041</FONT>     * &lt;p&gt; If {@link #evaluate(double[])} is used to compute the mean of an array<a name="line.41"></a>
<FONT color="green">042</FONT>     * of stored values, a two-pass, corrected algorithm is used, starting with<a name="line.42"></a>
<FONT color="green">043</FONT>     * the definitional formula computed using the array of stored values and then<a name="line.43"></a>
<FONT color="green">044</FONT>     * correcting this by adding the mean deviation of the data values from the<a name="line.44"></a>
<FONT color="green">045</FONT>     * arithmetic mean. See, e.g. "Comparison of Several Algorithms for Computing<a name="line.45"></a>
<FONT color="green">046</FONT>     * Sample Means and Variances," Robert F. Ling, Journal of the American<a name="line.46"></a>
<FONT color="green">047</FONT>     * Statistical Association, Vol. 69, No. 348 (Dec., 1974), pp. 859-866. &lt;/p&gt;<a name="line.47"></a>
<FONT color="green">048</FONT>     * &lt;p&gt;<a name="line.48"></a>
<FONT color="green">049</FONT>     *  Returns &lt;code&gt;Double.NaN&lt;/code&gt; if the dataset is empty.<a name="line.49"></a>
<FONT color="green">050</FONT>     * &lt;/p&gt;<a name="line.50"></a>
<FONT color="green">051</FONT>     * &lt;strong&gt;Note that this implementation is not synchronized.&lt;/strong&gt; If <a name="line.51"></a>
<FONT color="green">052</FONT>     * multiple threads access an instance of this class concurrently, and at least<a name="line.52"></a>
<FONT color="green">053</FONT>     * one of the threads invokes the &lt;code&gt;increment()&lt;/code&gt; or <a name="line.53"></a>
<FONT color="green">054</FONT>     * &lt;code&gt;clear()&lt;/code&gt; method, it must be synchronized externally.<a name="line.54"></a>
<FONT color="green">055</FONT>     * <a name="line.55"></a>
<FONT color="green">056</FONT>     * @version $Revision: 762116 $ $Date: 2009-04-05 12:48:53 -0400 (Sun, 05 Apr 2009) $<a name="line.56"></a>
<FONT color="green">057</FONT>     */<a name="line.57"></a>
<FONT color="green">058</FONT>    public class Mean extends AbstractStorelessUnivariateStatistic <a name="line.58"></a>
<FONT color="green">059</FONT>        implements Serializable {<a name="line.59"></a>
<FONT color="green">060</FONT>    <a name="line.60"></a>
<FONT color="green">061</FONT>        /** Serializable version identifier */<a name="line.61"></a>
<FONT color="green">062</FONT>        private static final long serialVersionUID = -1296043746617791564L;    <a name="line.62"></a>
<FONT color="green">063</FONT>        <a name="line.63"></a>
<FONT color="green">064</FONT>        /** First moment on which this statistic is based. */<a name="line.64"></a>
<FONT color="green">065</FONT>        protected FirstMoment moment;<a name="line.65"></a>
<FONT color="green">066</FONT>    <a name="line.66"></a>
<FONT color="green">067</FONT>        /** <a name="line.67"></a>
<FONT color="green">068</FONT>         * Determines whether or not this statistic can be incremented or cleared.<a name="line.68"></a>
<FONT color="green">069</FONT>         * &lt;p&gt;<a name="line.69"></a>
<FONT color="green">070</FONT>         * Statistics based on (constructed from) external moments cannot<a name="line.70"></a>
<FONT color="green">071</FONT>         * be incremented or cleared.&lt;/p&gt;<a name="line.71"></a>
<FONT color="green">072</FONT>         */<a name="line.72"></a>
<FONT color="green">073</FONT>        protected boolean incMoment;<a name="line.73"></a>
<FONT color="green">074</FONT>    <a name="line.74"></a>
<FONT color="green">075</FONT>        /** Constructs a Mean. */<a name="line.75"></a>
<FONT color="green">076</FONT>        public Mean() {<a name="line.76"></a>
<FONT color="green">077</FONT>            incMoment = true;<a name="line.77"></a>
<FONT color="green">078</FONT>            moment = new FirstMoment();<a name="line.78"></a>
<FONT color="green">079</FONT>        }<a name="line.79"></a>
<FONT color="green">080</FONT>    <a name="line.80"></a>
<FONT color="green">081</FONT>        /**<a name="line.81"></a>
<FONT color="green">082</FONT>         * Constructs a Mean with an External Moment.<a name="line.82"></a>
<FONT color="green">083</FONT>         * <a name="line.83"></a>
<FONT color="green">084</FONT>         * @param m1 the moment<a name="line.84"></a>
<FONT color="green">085</FONT>         */<a name="line.85"></a>
<FONT color="green">086</FONT>        public Mean(final FirstMoment m1) {<a name="line.86"></a>
<FONT color="green">087</FONT>            this.moment = m1;<a name="line.87"></a>
<FONT color="green">088</FONT>            incMoment = false;<a name="line.88"></a>
<FONT color="green">089</FONT>        }<a name="line.89"></a>
<FONT color="green">090</FONT>        <a name="line.90"></a>
<FONT color="green">091</FONT>        /**<a name="line.91"></a>
<FONT color="green">092</FONT>         * Copy constructor, creates a new {@code Mean} identical<a name="line.92"></a>
<FONT color="green">093</FONT>         * to the {@code original}<a name="line.93"></a>
<FONT color="green">094</FONT>         * <a name="line.94"></a>
<FONT color="green">095</FONT>         * @param original the {@code Mean} instance to copy<a name="line.95"></a>
<FONT color="green">096</FONT>         */<a name="line.96"></a>
<FONT color="green">097</FONT>        public Mean(Mean original) {<a name="line.97"></a>
<FONT color="green">098</FONT>            copy(original, this);<a name="line.98"></a>
<FONT color="green">099</FONT>        }<a name="line.99"></a>
<FONT color="green">100</FONT>    <a name="line.100"></a>
<FONT color="green">101</FONT>        /**<a name="line.101"></a>
<FONT color="green">102</FONT>         * {@inheritDoc}<a name="line.102"></a>
<FONT color="green">103</FONT>         */<a name="line.103"></a>
<FONT color="green">104</FONT>        @Override<a name="line.104"></a>
<FONT color="green">105</FONT>        public void increment(final double d) {<a name="line.105"></a>
<FONT color="green">106</FONT>            if (incMoment) {<a name="line.106"></a>
<FONT color="green">107</FONT>                moment.increment(d);<a name="line.107"></a>
<FONT color="green">108</FONT>            }<a name="line.108"></a>
<FONT color="green">109</FONT>        }<a name="line.109"></a>
<FONT color="green">110</FONT>    <a name="line.110"></a>
<FONT color="green">111</FONT>        /**<a name="line.111"></a>
<FONT color="green">112</FONT>         * {@inheritDoc}<a name="line.112"></a>
<FONT color="green">113</FONT>         */<a name="line.113"></a>
<FONT color="green">114</FONT>        @Override<a name="line.114"></a>
<FONT color="green">115</FONT>        public void clear() {<a name="line.115"></a>
<FONT color="green">116</FONT>            if (incMoment) {<a name="line.116"></a>
<FONT color="green">117</FONT>                moment.clear();<a name="line.117"></a>
<FONT color="green">118</FONT>            }<a name="line.118"></a>
<FONT color="green">119</FONT>        }<a name="line.119"></a>
<FONT color="green">120</FONT>    <a name="line.120"></a>
<FONT color="green">121</FONT>        /**<a name="line.121"></a>
<FONT color="green">122</FONT>         * {@inheritDoc}<a name="line.122"></a>
<FONT color="green">123</FONT>         */<a name="line.123"></a>
<FONT color="green">124</FONT>        @Override<a name="line.124"></a>
<FONT color="green">125</FONT>        public double getResult() {<a name="line.125"></a>
<FONT color="green">126</FONT>            return moment.m1;<a name="line.126"></a>
<FONT color="green">127</FONT>        }<a name="line.127"></a>
<FONT color="green">128</FONT>    <a name="line.128"></a>
<FONT color="green">129</FONT>        /**<a name="line.129"></a>
<FONT color="green">130</FONT>         * {@inheritDoc}<a name="line.130"></a>
<FONT color="green">131</FONT>         */<a name="line.131"></a>
<FONT color="green">132</FONT>        public long getN() {<a name="line.132"></a>
<FONT color="green">133</FONT>            return moment.getN();<a name="line.133"></a>
<FONT color="green">134</FONT>        }<a name="line.134"></a>
<FONT color="green">135</FONT>    <a name="line.135"></a>
<FONT color="green">136</FONT>        /**<a name="line.136"></a>
<FONT color="green">137</FONT>         * Returns the arithmetic mean of the entries in the specified portion of<a name="line.137"></a>
<FONT color="green">138</FONT>         * the input array, or &lt;code&gt;Double.NaN&lt;/code&gt; if the designated subarray<a name="line.138"></a>
<FONT color="green">139</FONT>         * is empty.<a name="line.139"></a>
<FONT color="green">140</FONT>         * &lt;p&gt;<a name="line.140"></a>
<FONT color="green">141</FONT>         * Throws &lt;code&gt;IllegalArgumentException&lt;/code&gt; if the array is null.&lt;/p&gt;<a name="line.141"></a>
<FONT color="green">142</FONT>         * &lt;p&gt;<a name="line.142"></a>
<FONT color="green">143</FONT>         * See {@link Mean} for details on the computing algorithm.&lt;/p&gt;<a name="line.143"></a>
<FONT color="green">144</FONT>         * <a name="line.144"></a>
<FONT color="green">145</FONT>         * @param values the input array<a name="line.145"></a>
<FONT color="green">146</FONT>         * @param begin index of the first array element to include<a name="line.146"></a>
<FONT color="green">147</FONT>         * @param length the number of elements to include<a name="line.147"></a>
<FONT color="green">148</FONT>         * @return the mean of the values or Double.NaN if length = 0<a name="line.148"></a>
<FONT color="green">149</FONT>         * @throws IllegalArgumentException if the array is null or the array index<a name="line.149"></a>
<FONT color="green">150</FONT>         *  parameters are not valid<a name="line.150"></a>
<FONT color="green">151</FONT>         */<a name="line.151"></a>
<FONT color="green">152</FONT>        @Override<a name="line.152"></a>
<FONT color="green">153</FONT>        public double evaluate(final double[] values,final int begin, final int length) {<a name="line.153"></a>
<FONT color="green">154</FONT>            if (test(values, begin, length)) {<a name="line.154"></a>
<FONT color="green">155</FONT>                Sum sum = new Sum();<a name="line.155"></a>
<FONT color="green">156</FONT>                double sampleSize = length;<a name="line.156"></a>
<FONT color="green">157</FONT>                <a name="line.157"></a>
<FONT color="green">158</FONT>                // Compute initial estimate using definitional formula<a name="line.158"></a>
<FONT color="green">159</FONT>                double xbar = sum.evaluate(values, begin, length) / sampleSize;<a name="line.159"></a>
<FONT color="green">160</FONT>                <a name="line.160"></a>
<FONT color="green">161</FONT>                // Compute correction factor in second pass<a name="line.161"></a>
<FONT color="green">162</FONT>                double correction = 0;<a name="line.162"></a>
<FONT color="green">163</FONT>                for (int i = begin; i &lt; begin + length; i++) {<a name="line.163"></a>
<FONT color="green">164</FONT>                    correction += (values[i] - xbar);<a name="line.164"></a>
<FONT color="green">165</FONT>                }<a name="line.165"></a>
<FONT color="green">166</FONT>                return xbar + (correction/sampleSize);<a name="line.166"></a>
<FONT color="green">167</FONT>            }<a name="line.167"></a>
<FONT color="green">168</FONT>            return Double.NaN;<a name="line.168"></a>
<FONT color="green">169</FONT>        }<a name="line.169"></a>
<FONT color="green">170</FONT>        <a name="line.170"></a>
<FONT color="green">171</FONT>        /**<a name="line.171"></a>
<FONT color="green">172</FONT>         * {@inheritDoc}<a name="line.172"></a>
<FONT color="green">173</FONT>         */<a name="line.173"></a>
<FONT color="green">174</FONT>        @Override<a name="line.174"></a>
<FONT color="green">175</FONT>        public Mean copy() {<a name="line.175"></a>
<FONT color="green">176</FONT>            Mean result = new Mean();<a name="line.176"></a>
<FONT color="green">177</FONT>            copy(this, result);<a name="line.177"></a>
<FONT color="green">178</FONT>            return result;<a name="line.178"></a>
<FONT color="green">179</FONT>        }<a name="line.179"></a>
<FONT color="green">180</FONT>        <a name="line.180"></a>
<FONT color="green">181</FONT>        <a name="line.181"></a>
<FONT color="green">182</FONT>        /**<a name="line.182"></a>
<FONT color="green">183</FONT>         * Copies source to dest.<a name="line.183"></a>
<FONT color="green">184</FONT>         * &lt;p&gt;Neither source nor dest can be null.&lt;/p&gt;<a name="line.184"></a>
<FONT color="green">185</FONT>         * <a name="line.185"></a>
<FONT color="green">186</FONT>         * @param source Mean to copy<a name="line.186"></a>
<FONT color="green">187</FONT>         * @param dest Mean to copy to<a name="line.187"></a>
<FONT color="green">188</FONT>         * @throws NullPointerException if either source or dest is null<a name="line.188"></a>
<FONT color="green">189</FONT>         */<a name="line.189"></a>
<FONT color="green">190</FONT>        public static void copy(Mean source, Mean dest) {<a name="line.190"></a>
<FONT color="green">191</FONT>            dest.incMoment = source.incMoment;<a name="line.191"></a>
<FONT color="green">192</FONT>            dest.moment = source.moment.copy();<a name="line.192"></a>
<FONT color="green">193</FONT>        }<a name="line.193"></a>
<FONT color="green">194</FONT>    }<a name="line.194"></a>




























































</PRE>
</BODY>
</HTML>
